Improvement in photographic camera-lenses



H. E. MEAD.

PHOT'UGRAPHIC CAMERA LENS.

NO.180,776. Patented Aug. 8.1876.

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75. JQ M.

N-PETEiS, PHOTO-LIYNOGRAFNER, WASHNGTON. D. C.

UNITED STATES PATENT OFFICE.

HENRY E. MEAD, OF JERSEY CITY, NEW JERSEY.

IMPROVEMENT IN PHOTOGRAPHIC CAMERA-LENSES.

Specification forming part of Letters Patent No. 180,776, dated August8, 1876; application filed May 8, 1876.

To all whom it may concern:

Be it known that I, HENRY E. MEAD, of Jersey City, county of Hudson,State of New Jersey, United States of America, have invented aPhotographic Camera-Lens, of which the following is a specification:

This invention consists of a camera-lens, the combinations in whichshall be composed of but three lenses, and which shall have no two ormore surfaces of said lenses cemented together.

In my improved lens, which is designed for a portraitlens, the frontcombination consists of a meniscus lens of crown-glass and aplaneconcave lens of flint glass, the two being sufficientlyover-corrected for actinic rays as to be finally corrected by the rearlens, which is a single meniscus, of crown-glass of different densityfrom the crown-glass used in the front combination.

The purpose gained by the following-described arrangement is, first, theproduction of a lens having the advantage of cheapness, as compared withthe combinations in general use, four lenses being generally employed 5second, it having no cementing material to deteriorate with age,climatic changes, or imperfect workmanship in the cementing.

To enable others skilled in the arts to make and use the same, I willnow describe its construction, reference being had to the annexeddrawings, in which- Figure 1 represents a vertical cross-section, andFig. 2 a modification of the same.

A represents the front lens of the combination, and is composed of ameniscus lens, a, and a planoconcave lens, I), the meniscus lens havingits convex surface outward or toward the object to be photographed, andthe planoconcave having either its concave surface, as

shown in Fig. 1, or plane surface, as shown in Fig. 2, resting againstthe concave side of the meniscus lens a, either position of thepiano-concave lens producing the purpose sought, though I havepreference for the position shown in Fig. 1. B is the rear lens, distantabout its diameter from the front lens, and consists of one meniscuslens, having its convex surface toward the ground glass of thecamera-box.

The radius of curvature in the front meniscus lens a is 3.07 inches forthe convex surface, and 13.213 inches for the concave surface. Theradius for concave surface of lens b is 7 inches. The radius of concavesurface of the rear lens B is 13.213 inches, and for the convex surface2.769 inches. The combined focuses from the back of rearlens is 5.5+

' inches. Those radii will be varied slightly to suit the purposes oflarger lenses and longer focus, the data given being for plates of fourand a fourth by five and a half inches, with lenses of one and a fourthinch in diameter.

By using the meniscus form of lens a with the plano-concave lens I) Iobtain a larger area and greater depth of sharp image than by using adouble-convex lens in place of the meniscus lens, or a double-concavelens in place of the piano-concave.

Having thus fully described my invention, what I claim as new, anddesire to secure by Letters Patent, is

The combination of the meniscus lens a and plane-concave lens b with themeniscus lens B, substantially as described, and for the purposespecified.

HENRY EDWIN MEAD.

Witnesses: R. H. ABERNETHY, T. L. LIEB.

